Proverbs 16:2 - Matthew Poole's English Annotations on the Holy Bible

All the ways of a man are clean in his own eyes; many men can easily flatter and deceive themselves into a good opinion of themselves, and of their own actions, though they be sinful. See below, Proverbs 16:25, and compare 1 Corinthians 4:4. The Lord weigheth, i.e. exactly knoweth, as men do the things which they weigh and examine, the spirits; the hearts of men, from which both men's actions, and the goodness and badness of them, in a great measure, proceed; their ends and intentions, their dispositions and affections, which are hid not only from others, but ofttimes from a man's self; whereby he is unfit to judge in his own cause, and easily mistaken, if he do not use great diligence and fidelity. In this last clause he intimates the reason why men deceive themselves in judging of their state and actions, because they do not search their own hearts.